Novel polymerization process using a catalyst system comprising an arylethylene oxide and oxygen



United States Patent NOVEL POLYMERIZATION PROCESS USING A CATALYSTSYSTEM COMPRISING AN ARYL- ETHYLENE OXIDE AND OXYGEN Alva F. Harris,Wilbraham, and Fernao Rodrigues, Ludlow, Mass., assignors to MonsantoCompany, a corporation of Delaware N0 Drawing. Filed Jan. 15, 1963, Ser.No. 251,482

12 Claims. (Cl. 260-880) This invention relates to the polymerization ofstyrenetype monomers and more particularly relates to the use of a novelcatalyst system in the polymerization of such monomers.

It is known that styrene-type monomers can be polymerized thermally orcatalytically to prepare polymers having molecular weights and residualmonomer contents which vary with certain reaction parameters, e.g., thecatalyst concentration, the time and temperature of the reaction, etc.It is also known that the product normally has an undesirably highresidual monomer content when the parameters of a mass polymerizationprocess are controli'ed so as to prepare a molding-grade polystyrene,i.e., a polystyrene having a Staudinger average molecular weight in therange of about 40,000=100,000.

As shown in US. Patent 2,675,362, certain catalysts make it possible touse a mass polymerization process in preparing molding-grade polystyrenehaving a residual monomer content as low as 0.35-0.5%, and the producthas improved physical and molding properties because of the reduction inresidual monomer content. It would obviously be desirable to find acatalyst capable of reducing the residual monomer content to even lowerlevels with out otherwise causing degradation of the product because of(1) the greater improvement in the physical and molding properties ofthe polymer which could result from the greater reduction in residualmonomer content and (2) the decreased likelihood of reaching undesirablyhigh levels with the anomalously higher-than-normal residual monomercontents which are occasionally encountered when styrene-type monomersare mass polymerized on a commercial scale.

An object of the invention is to provide a novel process forpolymerizing styrene-type monomers.

Another object is to provide a process for polymerizing styrene-typemonomers in the presence of a novel catalyst system.

A further object is to provide a mass process for polymerizingstyrene-type monomers to moldable polymers containing a minimum amountof residual monomer.

These and other objects are attained by (1) dissolving a catalyticmixture of ,an arylethylene oxide, oxygen, and a monocarboxylic acidhaving a dissociation constant not higher than 1.0 at 25 C. in apolymerizable material comprising a monovinyl aromatic hydrocarbon and/or an ar-halo monovinyl aromatic hydrocarbon and (2) heating topolymerize the polymerizable material, the polymerization beingconducted at 180-220 C. during the finishing stage of the reaction.

When desired, the catalyst mixture can also include a monomer-solubleperoxy compound having a half-life of at least 10 hours in benzene at100 C. This optional ingredient is particularly apt to be desirable whenthe invention is applied to a mass polymerization process utilizing thetime-temperature cycle which is hereinafter defined as the cycle whichshould be employed when the reaction is intended to produce a moldablepolymer having a minimum residual monomer content.

The following examples are given to illustrate the invention and are notintended as a limitation thereof. In the reactions described in theseexamples (1) quantities mentioned are quantities by weight unlessotherwise spec- "ice ified, (2) the monovinyl aromatic monomers employedas starting materials are commercially-supplied monomers containing 0.00l0.0015% t-butyl catechol and varying amounts of the impurities normallypresent in commercially-supplied styrene-type monomers, and (3) aliquotsof the same monomer sample are polymerized in any series of reactionsproposed for direct comparison of results.

EXAMPLE I Part A .-Contr0l Dissolve 0.04 part of di-t-butyl peroxide and0.28 part of stearic acid in parts of styrene. Purge the reaction vesselwith nitrogen and heat at 90 C. for 24 hours to convert about 32% of thestyrene to polymer. Then gradually raise the reaction temperature to 190C. over a period of 4.75 hours and maintain the temperature at 190 C.for an additional 4 hours. The product has a Staudinger averagemolecular weight in the range of 40,00070,000 and a residual monomercontent of 1.40%

Part B Prepare six products by repeating Part Aexcept for alsodissolving 0.01 part of styrene oxide and varying amounts of oxygen inthe monomer. Each of the products has a Staudinger average molecularweight in the range of 40,00070,000. The residual monomer contents ofthe products, together with the amounts of oxygen employed in theirpreparation, are shown below.

Residual Reaction Number Oxygen (parts) Monomer (percent) Asdemonstrated in the preceding example, the addition of 0.01 part ofstyrene oxide and 0.00l0.03 part of oxygen to a di-t-butylperoxide/stearic acid catalyst mixture can efiect a 5292% decrease inthe residue monomer content of the product. Even greater decreases inresidual monomer content are effected when 0.1 part of styrene oxide isused in conjunction with 0.001-003 part of oxygen. Similar results areobserved when Example I is repeated except that:

(1) No di-t-butyl peroxide or other peroxy compound is employed,

(2) The time-temperature cycle employed for the reaction is (a) 24 hoursat 90 C., followed by 3.5 hours at 90-185 C., followed by 1 hour at C.,(b) 24 hours at 90 C., followed by 6.25 hours at 90-185 C., followed by1.5 hours at 185 C. or (c) 12 hours at l1090 C., followed by 4.5 hoursat 90l90 C., followed by 3 hours at C.,

(3) The 0.001-0.1 part of styrene oxide is replaced with 0.0010.l partof o-methylstyrene oxide, p-chlorostyrene oxide, 2,5-dichlorostyreneoxide, or p-t-butylstyrene oxide,

(4) The 0.28 part of stearic acid is replaced with 0.4 part of stearicacid, 0.1 part of benzoic acid, or 0.06 part of acetic acid, or

(5) The 10 parts of styrene are replaced with 100 parts ofp-chlorostyrene, 100 parts of a mixture of o-, m-, and p-methylstyrenes,a mixture of 85 parts of styrene and 15 parts of acrylonitrile, amixture of 80 parts of styrene and 20 parts of methyl methacrylate, amixture of 75 parts of styrene and 25 parts of alpha-methylstyrene, or asolution of 10 parts of a rubbery butadiene-styrene (75:25) copolymer in100 parts of styrene.

EXAMPLE II Control Repeat Example I except for employing no stearic acidas a catalyst component. The residual monomer contents of the productsprepared in the presence of the dit-butyl peroxide/styrene oxide/oxygencatalyst systems are substantially the same as the residual monomercontent of the product prepared in the presence of the di-tbutylperoxide catalyst.

EXAMPLE III Control Repeat Example I except for conducting the reactionsisothermally at 90 C. The residual monomer contents of the productsprepared in the presence of the di-t-butyl peroxide/stearic acid/styreneoxide/oxygen catalyst systems are substantially the same as the residualmonomer content of the product prepared in the presence of thedi-t-butyl peroxide/stearic acid catalyst system.

The process of the invention comprises (1) dissolving a catalyst mixtureconsisting of an arylethylene oxide, oxygen, a weak organic acid, and anoptional peroxy compound in a polymerizable material comprising astyrene-type monomer and (2) heating to cause polymerization, theprocess being conducted at 180-220 C. during the finishing stage of thereaction.

The arylethylene oxide employed in the practice of the invention is acompound corresponding to the formula:

wherein R is an aryl radical, e.g., phenyl, alkylphenyl, halophenyl,naphthyl, alkylnaphthyl, halonaphthyl, biphenyl, etc. Such compounds,when not easily available, can be prepared by the direct oxidation ofthe corresponding RCH:CH compound with, e.g., perbenzoic acid, or by anyother suitable technique. Various methods of preparing alkylene oxidesare disclosed, e.g., in Migrdichian, Organic Synthesis, vol. 1, ReinholdPublishing Corporation, New York (1957), on pages 80-87.

Exemplary of utilizable arylethylene oxides are styrene oxide;ar-alkylstyrene oxides, such as m-, and pmethylstyrene oxides,p-ethylstyrene oxide, pt-butylstyrene oxide, etc.; ar-halostyreneoxides, such as o-, m-, and p-chlorostyrene oxides, p-bromostyreneoxide, 2,5- dichlorostyrene oxide, 2,4-dichlorostyrene oxide, 2-ch1oro-4-methylstyrene oxide, etc. ar-alkoxystyrene oxides, such asp-methoxystyrene oxide; etc.; naphthylethylene oxide; ar-substitutednaphthylethylene oxides, such as the archloro andar-methylnaphthylethylene oxides, etc., and mixtures thereof. Although,as demonstrated, these utilizable compounds can bear a plurality ofar-substituents, arylethylene oxides having ar-substituents in both ofthe positions ortho to the epoxyethyl group will not ordinarily be foundeffective in the practice of the invention except when they are used inconjunction with the more reactive arylethylene oxides which are free ofsubstituents in at least one of the ortho positions. Styrene oxide isthe preferred arylethylene oxide.

The reaction mixture should contain at least 0.0001% of the arylethyleneoxide, based on the weight of polymerizable material, and usuallycontains not more than 2% of the arylethylene oxide. Concentrationslower than 0.0001% are ineffective in the practice of the invention;concentrations higher than 2% can be employed without ill effect but donot appear to offer any advantage over concentrations of 12%. Ordinarilythe reaction mixture will contain 0.00l1% of the arylethylene oxide Whenthe optional organic peroxy compound is employed as a catalyst componentand 0.012% of the arylethylene oxide when no organic peroxy compound isemployed.

The oxygen employed as a catalyst component is used in concentrations ofabout 0.0010.03%, preferably about 0.010.02%, based on the Weight ofpolymerizable material. Pure oxygen does not have to be used, since airis also suitable.

The Weak organic acid employed as a catalyst component can be anymonocarboxylic acid having a dissociation constant not higher than 1.0l0 at 25 C. Among the particularly suitable acids are acetic, hexanoic,benzoic, phenylacetic, isopropylbenzoic, and hexahydrobenzoic acids and,as a preferred embodiment of the invention, alkanoic acids containingl2-20 carbon atoms (i.e., lauric, tridecanoic, myristic, pentadecanoic,palmitic, margaric, stearic, nonadecanoic, and eicosanic acids). Stearicacid is especially preferred because of the brilliance it imparts to themolded polymers.

The reaction mixture should contain at least 0.05% of the weak organicacid, based on the weight of polymerizable material, and usuallycontains not more than 1% of the acid. Within the range of 0.05-1% andat higher concentrations, variation in the concentration of a particularacid seems to have no substantial effect on the molecular weights andresidual monomer contents of the polymers formed by the reaction, but itis usually preferred to avoid concentrations higher than 1% in order toavoid undue yellowing of the polymer. Ordinarily the reaction mixturewill contain 01-06% of the acid.

The optional component of the catalyst mixture can be anymonomer-soluble peroxy compound having a halflife of at least 10 hoursin benzene at C. Utilizable peroxy compounds include, e.g., hydrogenperoxide, di-tbutyl diperphthalate, t-butyl peracetate, t-butylperbenzoate, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,t-butyl hydroperoxide, cumene hydroperoxide, p-menthane hydroperoxide,cyclopentane hydroperoxide, diisopropylbenzene hydroperoxide,p-t-butylcumene hydroperoxide, pinane hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide, etc., and mixtures thereof.

The reaction mixture can contain up to 0.1% of the peroxy compound,based on the weight of polymerizable material. This optional componentmay be found desirable when a substantial amount of the polymerizationis to be accomplished at temperatures at which such peroxy compounds areeffective, eg, when the process utilizes the time-temperature cyclehereinafter defined as the cycle to be employed in a mass process whenthe product is to be a moldable polymer containing a minimum amount ofresid ual monomer. When included as a catalyst component, the peroxycompound is usually employed in concentrations of 0.010.l%, preferably0.01-0.05

The catalyst mixtures of the invention are used in the polymerization ofpolymerizable materials comprising a monovinyl aromatic hydrocarbonand/or an ar-halo monovmyl aromatic hydrocarbon, e.g. styrene; vinylnaphthalene; ar-alkyl styrenes, such as o-, m-, and p-methylstyrenes,ar-ethylstyrenes, etc.; o-chlorostyrene; p-bromostyrene;2-chl0ro-4-methylstyrene, etc., and mixtures thereof. Such moniovinylaromatic monomers, as is well known, normally contain minor amounts ofimpurities formed as by-products of the monomer synthesis or accumulatedduring storage. Since the presence of these impurities appears to bemore desirable than undesirable in the practice of the invention, theyare not removed from the monomers prior to polymerization except whenthe particular application for which the product of the polym erizationis intended requires the removal of one or more particular impuritiesknown to contribute properties which would be undesirable in thatapplication, e.g., excessive amounts of dissolved oxygen are removedwhen the application will not tolerate the degree of yelliowness thatwould be contributed to the polymer by large amounts of oxygen.

The monovinyl aromatic monomer may constitute the only component of thepolymerizable material or may be in admixture with lesser amounts of oneor more copolymerizable monomers, such as acrylonitrile;methacrylonitrile; an alkyl methacrylate, e.g. the methyl, ethyl,propyl, and butyl methacrylates; the corresponding alkyl acrylates;alpha-alkylstyrenes, e.g., alpha-methylstyrene, alpha-ethylstyrene,alpha-methyl-p-methylstyrene, etc.

When desired, the polymerizable material can have a rubbery conjugated1,3-diene polymer (e.g., natural rubber, p'olybutadiene, polyisoprene,copolymers of butadiene and/ or isoprene with lesser amounts ofcomonomers such as styrene, acrylonitrile, methyl methacrylate, etc.)dissolved therein, ordinarily in amounts of 125%, based on the weight ofpolymerizable material. Also, the reaction mixture can contain otheroptional ingredients such as plasticizers, mineral oils, stabilizers,etc.

The process of the invention is conducted at ISO-220 0, preferablyISO-200 C., during the finishing stage of the reaction because of theineifectiveness of the arylethylene oxide/oxygen/weak organic acidcatalyst systems at lower temperatures. Prior to the finishing stage,the reaction can be conducted under any conditions suitable to thetechnique employed (e.g., a mass, suspension, batch, or continuoustechnique) and to the type of product desired. Thus, the process may beconducted at ISO-220 C. throughout the reaction when a comparatively lowmolecular weight product is desired, whereas lower temperatures, e.g.,90 C., will be maintained for as long as is practical when a highermolecular weight pnoduct is desired. Methods of varying polymerizationconditions to obtain a particular type of product are, of course,already well known to the art. As will be readily understood, the timeat which the reaction temperature should be raised to the finishingtemperature will vary with the conditions which have been employedduring the earlier stages of the reaction, since some of theseconditions normally lead to higher degrees of conversion than others.Ordinarily, the finishing temperature of ISO-220 C. will be utilized atleast during the stage of the reaction after 98% conversion of monomerto polymer.

A preferred embodiment of the invention is the use of the arylethyleneoxide/oxygen/weak organic acid catalyst systems in the masspolymerization of styrene-type monomers to moldable polymers having aminimum residual monomer content. In order for the product of this massprocess to have the desired properties, a fairly specifictimetemperature cycle should be employed. In the first stage of thereaction, polymerization is conducted at 75-125 C. for about 6-24 hoursuntil 15-45% of the monomer has been converted to polymer; in the secondstage, the reaction temperature is gradually raised from 75-95 C. toISO-200 C. over a period of about 3-7 hours; in the final stage, thereaction temperature is maintained at 180- 200 C. for about 0.5-5 hours.

The manner of manipulating the reaction temperature during the firststage of the reaction in order to be in the 75-95 C. range for thebeginning of the second stage of the reaction is not critical, e.g., aninitial temperature of about 100-125 C. can be gradually lowered to75-95 C. during the first stage of the reaction or the temperature canbe maintained at 75-95 C. throughout the first stage of the reaction,etc. According to a particularly preferred embodiment of the invention,the reaction mixture is initially heated to 105-115 C. and maintained ata temperature gradually lowered to about 90 C. until about 25-45%conversion to polymer is obtained, after which the temperature isgradually raised to 180-200 C. over a period of about 3-7 hours and thenmaintained at 180-200" C. for about 2-5 hours to complete the reaction.Especially good results are also obtained by initially heating thereaction mixture at 90 C. to about 25-35% conversion, then heating at atemperature gradually raised to 180200 6 C. over a period of about 4-5hours, and finally heating at ISO-200 C. for 2-4 hours.

Although also generally useful as a new catalytic method of polymerizingstyrene-type monomers, the present invention is particularlyadvantageous in that it permits the formaiton by a mass process ofmoldable polystyrenetype materials having lower residual monomercontents than the comparable polymers of the prior art. The reducedresidual monomer content improves the physical and molding properties ofthe polymers.

It is obvious that many variations can be made in the products andprocesses set forth above without departing from the spirit and scope ofthis invention.

What is claimed is:

1. A process which comprises (1) dissolving a catalyst mixtureconsisting of:

(a) at least 0.0001 part by weight of an arylethylene oxidecorresponding to the formula:

0 ROfi CHz wherein R is an aryl radical of the group consisting ofphenyl, alkylphenyl, alk oxypheny-l, halophenyl, naphthyl,alkylnaphthyl, halonaphthyl, and biphenyl radicals,

(b) about 0.001-0.03 part by weight of oxygen,

(c) 0.05-1 part by weight of a'monocarboxylic acid having a dissociationconstant not higher than 1.0 10 at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the groupconsisting of hydrogen peroxide and an organic peroxy compound having ahalf-life of at least 10 hours in benzene at C.

in 100 parts by weight of a polymerizable material comprising at least amajor portion of a monovinyl aromatic monomer of the gnoup consisting ofa monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatichydrocarbon, and mixtures thereof and (2) heating to polymerize thepolymerizable material; said process being conducted at -220 C. duringthe finishing stage of the reaction.

2. A mass polymerization process which comprises (1) dissolving acatalyst mixture consisting of:

(a) at least 0.0001 part by weight of an arylethylene oxidecorresponding to the formula:

0 R-C-\CH2 wherein R is an aryl radical of the group consisting ofphenyl, alkylphenyl, allcoxyphenyl, halophenyl, naphthyl, alkylnaphthyl,halonaphthy-l, and biphenyl radicals,

(b) about 0001-003 part by weight of oxygen,

(c) 0.05-1 part by weight of a monocarboxylic acid having a dissociationconstant not higher than 1.0 l0- at 25 C., and

(d) up to 0.1 part by weight of a peroxy compound of the groupconsisting of hydrogen peroxide and an organic peroxy compound having ahalf-life of at least 10 hours in benzene at 100 C.

in 100 parts by weight of a polymerizable material comprising at least amajor proportion of a monovinyl aromatic monomer of the group consistingof a monovinyl aromatic hydrocarbon, an ar-halo monovinyl aromatichydrocarbon, and mixtures thereof, (2) heating the polymerizablematerial at 75125 C. until 15-45% conversion to polymer is obtained, thetemperature being so regulated as to be in the 75-95 C. range when thisconversion is obtained, (3) gradually raising the reaction temperatureto 180-200 C. over a period of about 3-7 hours, and (4) maintaining thereaction temperature at 180-200 C. for about 0.5-5 hours.

3. The process of claim 2 wherein the polymerizable material is styrene.

4. The process of claim 2 wherein the polymerizable material is amixture of styrene and alpha-methylstyrene.

5. The process of claim 2 wherein the polymerizable material is amixture of styrene and acrylonitrile.

6. The process of claim 2 wherein the polymerizable material is amixture of styrene and methyl methacrylate.

7. The process of claim 2 wherein the polymerizable material contains adissolved rubbery conjugated 1,3-diene polymer.

8. The process of claim 2 wherein the arylethylene oxide is styreneoxide.

9. The process 10f claim 2 wherein the monocarboxylic acid is analkanoic acid containing 12-20 carbon atoms.

10. The process of claim 2 wherein the catalyst mixture consists of (a)0.01-2 parts by weight of the arylethylene oxide, (b) 0.01-0.02 part byweight of oxygen, and (c) 0.1-0.6 part by weight of a monocarboxylicacid having a dissociation constant not higher than 1.0 10 at 25 C.

11. The process of claim 2 wherein the catalyst mixture consists of (a)0.001-1 part by weight of the arylethylene oxide, (b) 0.01-0.02 part byweight of oxygen, (c) 0.1-0.6 part by weight of a monocarboxylic acidhaving a dissociation constant not higher than 1.0 10- at 25 C., and (d)0.01-0.1 part by weight of a peroxy compound of the group consisting ofhydrogen peroxide and an organic peroxy compound having a half-life ofat least 10 hours inbenzene at 100 C.

12. A mass polymerization process which comprises (1) dissolving acatalyst mixture consisting of (a) 0.001- 1 part by weight of styreneoxide, (b) 0.01-0.02 part by weight of oxygen, (0) 0.1-0.6 part byweight of stearic acid, and (d) 0.01-0.05 part by weight of di-t-butylperoxide in parts by weight of styrene, (2) heating the styrene to -115C. and then gradually lowering the temperature to about 90 C. to obtain25-45% conversion to polymer, (3) gradually raising the temperature to180200 C. over a period of about 3-7 hours, and (4) maintaining thereaction temperature at 180-200 C. for 2-5 hours.

References Cited by the Examiner UNITED STATES PATENTS 2,569,506 10/1951Vandenberg 260-935 2,675,362 4/1954 Shusman 260-23 2,886,553 5/1959Stein et a1 26093.5

FOREIGN PATENTS 807,739 I/ 1959 Great Britain. 1,035,366 7/1958 Germany.1,088,230 9/ 1960 Germany.

JOSEPH L. SCHOFER, Primary Examiner.

DONALD E. CZAJA, Examiner.

1. A PROCESS WHICH COMPRISES (U) DISSOLVING A CATALYST MIXTURECONSISTING OF: (A) AT LEAST 0.0001 PART BY WEIGHT OF AN ARYLETHYLENEOXIDE CORRESPONDING TO THE FORMULA: